The present invention relates generally to a compressible fluid suspension unit. More specifically, the present invention relates to a suspension strut for assembly in a vehicle suspension system wherein such suspension system is subjected to large weight differentials resulting from loaded and unloaded conditions of the vehicle.
To improve riding qualities of any motor vehicle, it is desirable to provide suspension springs that have a low spring rate. These low spring rates result in soft springs which cushion the vehicle ride but which have the disadvantage of causing excessive and objectionable deflection of a vehicle body when it is loaded in an extreme manner.
Because of the massive loads carried by off-highway vehicles such as large earth moving dump trucks and the like to which the present invention is applicable, the weight differential between the loaded and unloaded conditions varies greatly. Consequently, a suspension designed to ride well in the loaded condition would be unduly stiff when riding empty. Conversely, a suspension designed to ride well in the unloaded condition will be unduly soft when riding in the loaded condition which in turn results in well recognized safety and operational problems with respect to the vehicle.
The problem therefore in providing a suspension system that will accommodate the off-highway vehicle in the loaded condition is that of having the vehicle subjected to an unduly stiff suspension and ride during unloaded use. This results in a hard ride which is obviously uncomfortable to the driver and passengers in view of the inability of the suspension system to absorb road shock which in turn results in excessive stress being transmitted throughout the entire vehicle structure. This condition has obvious deleterious affects on the vehicle body and tires, the latter being subjected to excessive sidewall flexing, bruising and heat buildup which in turn decreases their useful life. The above situation indicates the need for a suspension system that provides similar ride characteristics in an off-highway vehicle at both ends of its load scale, that is in a loaded and unloaded condition. Such characteristics are provided by the double liquid spring arrangement to be described in which two separate spring constants are provided for accommodating the various loading conditions of an off-highway vehicle.
The prior art includes various types of suspension springs such as leaf spring, rubber, pneumatic and single rate or single stage liquid springs. However, none of the prior art structures have been able to provide a spring which will accommodate the requirements of an off-highway vehicle operation contemplated by the present invention in which a large weight differential is encountered through loaded and unloaded conditions. Correspondingly, it is necessary that a spring or suspension system having such a capability be of reasonable size so as to be copacetic within the general confines of a vehicle structure, none of which has been effectively accomplished in the prior art structures.